The invention relates to a method of operating a printing machine, more particularly, a printing machine that includes a printing form or plate cylinder and an inking unit for inking the cylinder, the inking unit having at least one inking unit roller rotatably driven at a speed different from the peripheral speed of the printing form cylinder. The invention further relates to a printing machine for performing the aforementioned method, more particularly, a printing machine that includes a printing form or plate cylinder and an inking unit for inking the cylinder, the inking unit having at least one inking unit roller rotatably driven at a speed different from the peripheral speed of the printing form cylinder.
The published European Patent Document EP 0 813 963 A1 describes an offset printing device wherein ink applicator rollers are driven frictionally at differential speeds different from the peripheral speed of a form or plate cylinder by formlockingly or positively driven inking rollers, and it is possible for the formlockingly driven inking rollers to be changed over from a differential speed to a synchronous speed relative to the peripheral speed of the form cylinder, depending upon the subject and/or printing material to be processed. In this regard, it is noted that a formlocking connection is one which connects two elements together due to the shape of the elements themselves, as opposed to a forcelocking connection, which locks the elements together by force external to the elements.
Although the wear behavior of a dry planographic printing plate can be improved thereby in cases wherein no contamination or only slight contamination occurs, no different operating states of the inking unit are taken into consideration at the time when a shift or change-over is made to the synchronous speed.
For example, no consideration is given as to whether the inking rollers are rotating at the synchronous speed or at the differential speed that differs from the plate-cylinder speed, before ink runs into the inking unit or after an inking-unit cleaning.
Consequently, the disadvantages described hereinbelow result.
If the inking unit of the offset printing device is to be cleaned, it is possible for the ink applicator rollers to rest on the plate cylinder during the cleaning, so that the printing plate is indirectly cleaned simultaneously via the inking unit. Cleaning can be performed in a number of washing cycles, respectively, including feeding washing fluid into the inking unit, and subsequent doctoring of the washing fluid/printing ink mixture. The inking unit and the printing plate or form increasingly cleaner from washing cycle to washing cycle, as a result of which, rubber-covered inking-unit rollers are subjected to rapidly increasing wear because of the vanishing lubricating action of the printing ink between the inking unit rollers. Because the formlockingly or positively driven inking rollers of the offset printing device belonging to the prior art rotate at the differential speed during the cleaning, each ink applicator roller is subjected to increased abrasion that is virtually dry at the end of the cleaning, both at the first slippage point thereof formed with the plate cylinder, and at the second slippage point thereof formed with the inking roller driving the ink applicator roller frictionally. When special inks and the like specific to a printing job are used, inking units have to be cleaned several times a day, so that the wear stresses associated with each cleaning operation add up and, after a comparatively short service life, make it necessary to replace the worn inking-unit roller.
If ink is to be introduced into the inking unit of this offset printing device, it is conceivable to bring the ink applicator rollers thereof into contact with the printing plate only after the infeeding of the ink, however, in this case, the problem of dry abrasion of rubber-covered rollers in the inking unit likewise arises if a number of the formlockingly or positively driven inking rollers rotate at differential speeds which differ in amount relative to one another. If the inking unit runs for a given time without printing ink, and therefore nonlubricated, before entry of the ink, the formlockingly or positively driven inking rollers gradually wear away the rubber-covered rollers arranged therebetween in the roller train of the inking unit. The two slippage points are formed, in this case, by the respective rubber-covered roller together with a first and a second adjacent roller engaging the rubber-covered roller. The adjacent rollers can be directly the two inking rollers driven formlockingly or positively at different differential speeds, or rollers arranged between the formlockingly or positively driven inking rollers and the rubber-covered inking roller.
In a further offset printing device described in the published German Patent Document DE 196 25 020 A1, the problems described hereinbefore and caused by inking unit rollers stripping or running blind occur in the same way.
It is thus an object of the invention to provide an improved method for low-wear operation of a printing machine and to provide a printing machine by which the low-wear operation method is performed.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a method of operating a printing machine including a printing form cylinder and an inking unit for inking the cylinder, the inking unit having at least one inking unit roller rotatably driven at a differential speed different from the peripheral speed of the printing form cylinder, which comprises rotatably driving the at least one inking unit roller at the differential speed and at a relative speed that is different from the peripheral speed of the printing form cylinder, in time-dependence upon various operating states of the inking unit.
In accordance with another mode, the method of the invention includes driving the inking unit roller at the differential speed and at a synchronized speed in time-dependence upon various operating states of the inking unit.
In accordance with a further mode, the method of the invention includes driving the inking unit roller at the differential speed in a first operating state and at the synchronized speed in a second operating state, depending upon the ink content of the inking unit, which is different in the respective operating states.
In accordance with an added mode, the method of the invention includes driving the inking unit roller at the synchronized speed when the inking unit is running virtually without ink, and at the differential speed when the inking unit is running with ink.
In accordance with an additional mode, the method of the invention includes driving the inking unit roller at the differential speed and at a different differential speed in time-dependence upon the various operating states of the inking unit.
In accordance with yet another mode, the method of the invention includes driving the inking unit roller at the differential speed in a first operating state, and at the different differential speed in a second operating state, depending upon the ink content of the inking unit, which is different in the respective operating states.
In accordance with yet a further mode, the method of the invention includes driving the inking unit roller at the differential speed when the inking unit is running with ink, and driving the inking unit roller at the different differential speed when the inking unit is running virtually without ink.
In accordance with yet an added mode, the method of the invention includes changing-over the peripheral speed of the. inking unit roller in time-dependence upon an ink infeed into the inking unit.
In accordance with yet an additional mode, the method of the invention includes changing-over the peripheral speed of the inking unit roller in time-dependence upon a cleaning of the inking unit.
In accordance with a second aspect of the invention, there is provided a printing machine having a printing form cylinder and an inking unit for inking the cylinder, the inking unit comprising at least one inking unit roller drivable by a rotary drive at a differential speed with respect to the peripheral speed of the printing form cylinder, the rotary drive of the at least one inking unit roller being constructed so as to be changeable-over in time-dependence upon various operating states of the inking unit, so that the rotary drive drives the at least one inking unit roller at the differential speed in a first operating state, and drives the at least one inking unit roller at another relative speed in a second operating state.
In accordance with another feature of the invention, the printing machine includes an electronic control for Changing-over the rotary drive of the inking unit roller from the differential speed to the other relative speed and/or from the other relative speed to the differential speed, depending upon the quantity of ink in the inking unit during the operating states.
In accordance with a further feature of the invention, the electronic control device is linked controllingly with an infeed device for feeding printing ink to the inking unit, and serves for changing-over the rotary drive of the at least one inking unit roller in time-dependence for activating the infeed device.
In accordance with an added feature of the invention, the electronic control device is linked controllingly with a cleaning device for removing the printing ink from the inking unit, and serves for changing-over the rotary drive of the inking unit roller in time-dependence for activating the cleaning device.
In accordance with an additional feature of the invention, the rotary drive of the inking unit roller is an individual electric motor drive controllable independently of a rotary drive of the printing form cylinder.
In accordance with yet another feature of the invention, the other relative speed of the inking unit roller corresponds to the peripheral speed of at least one other roller of the printing machine.
In accordance with yet a further feature of the invention, the printing machine includes a rotary drive for driving the at least one other roller, the rotary drive of the at least one other roller being controllable independently of a rotary drive of the plate cylinder, and being an individual electric motor drive linked controllingly with the electronic control.
In accordance with yet an added feature of the invention, the rotary drive of the at least one other roller is Changeable-over in a manner coordinated with the rotary drive of the at least one inking unit roller.
In accordance with yet an additional feature of the invention, the at least one other roller is an inking unit roller of the inking unit.
In accordance with an alternative feature of the invention, the at least one other roller is a dampening unit roller of a dampening unit for dampening the printing form cylinder.
In accordance with a further alternative feature of the invention, the at least one other roller is a distributor roller oscillatable in the axial direction thereof.
In accordance with another alternative feature of the invention, the at least one inking unit roller is a distributor roller oscillatable in the axial direction thereof.
In accordance with a concomitant feature of the invention, the at least one inking unit roller and the at least one other roller are engageable simultaneously with one and the same roller.
Thus, the method according to the invention for operating a printing machine including a printing plate cylinder and an inking unit which inks the latter, at least one inking unit roller being driven in rotation at a differential speed with respect to the peripheral speed of the printing plate cylinder, is distinguished by the fact that the at least one inking unit roller is selectively driven at the differential speed and at a relative speed that is different from the peripheral speed of the printing plate cylinder, based upon the timing of various operating states of the inking unit.
Due to the driving of the one inking unit roller or the plurality of inking unit rollers, during the various operating states of the printing unit, at the tangential relative speeds which, as referred to the peripheral and tangential speed, respectively, of the printing form cylinder, are matched to the various operating states of the inking unit, a much greater service life of the soft rubber-covered rollers provided in the inking unit is achieved than in the operating methods according to the prior art.
For example, it is possible to drive the at least one inking unit roller or the several inking unit rollers at a peripheral speed which differs from the peripheral speed of the printing plate cylinder by a specific difference during a first operating state of the inking unit, and to drive it at a peripheral speed which differs from the peripheral speed of the printing plate cylinder by another difference during a second operating state of the inking unit. It is also possible to drive the one inking unit roller or the several inking unit rollers at a peripheral speed which differs from the peripheral speed of the printing plate cylinder in the first operating state of the inking unit and to drive it at a peripheral speed which is equal to the peripheral speed of the printing plate cylinder in the second operating state of the inking unit.
Managing the peripheral speed of the one inking unit roller or of the plurality of inking unit rollers in a manner coordinated with the operating states of the inking unit is therefore assured in the event of a change in the inking unit from the first to the second operating state, by increasing or reducing the relative speed in relation to the peripheral speed of the printing plate cylinder.
The action of changing-over or converting the inking unit from the first to the second operating state may require a transition state, which begins with the end of the first operating state and ends with the beginning of the second operating state.
For example, the first operating state may be such wherein the inking unit rollers of the inking unit rotate without infeeding ink thereto. As the printing ink is fed into the inking unit, the first operating state ends and the transition state begins, during which the inking unit is gradually filled with the printing ink. When the inking unit has been filled with the quantity of ink required for the inking of a printing form on the printing form cylinder, the transition state ends and the second operating state begins, the latter operating state being distinguished by a fully filled inking unit and by the fact that, during which, the printing plate is inked and can be used for printing. At the beginning, during or at the conclusion of the transition state, the action of Changing-over the peripheral speed of the one inking unit roller or of the plurality of inking unit rollers can be performed, so that coordination of the timing in relation to the following second operating state is provided.
If the inking unit is filled very quickly with the printing ink during the infeeding of the ink, and the inking unit roller to be changed-over, respectively, within an inking unit roller train, of which the inking unit is composed, is arranged very close to an infeeding device for feeding the printing ink to the printing unit, the action of changing-over the peripheral speed of the inking unit roller can be performed at the beginning of the transition state and, for example, simultaneously with a control signal which activates the infeeding device.
If the inking unit is filled only very slowly with the printing ink, and the inking unit roller to be changed-over, respectively, is located at a very great distance from the infeeding device, the action of changing-over the inking unit roller can be performed at the end of the transition state and, for example, simultaneously with a control signal which brings about the second operating state. This control signal can activate a dampening unit, which then pre-dampens the printing form and/or the inking unit. The control signal can also activate the inking unit, which then inks the printing form.
However, the transition of the inking unit from the first operating state to the second operating state can also be associated with emptying the ink from the inking unit. In this case, in the first operating state, the inking unit runs with a full supply of ink. The first operating state ends when cleaning of the inking unit begins, during which the printing ink in the inking unit is gradually removed from the inking unit during what constitutes the transition state. The end of the transition state, i.e., the conclusion of the cleaning of the inking unit, marks the beginning of the second operating state, during which the inking unit runs without having a supply of printing ink. The action of changing-over the inking unit roller or inking unit rollers can be performed at the beginning, during or at the conclusion of this transition state.
For example, in the case wherein a very small quantity of ink is present in the inking unit, and the inking unit roller to be changed-over in the inking unit roller train is arranged very close to the cleaning device, the action of changing-over the roller can be performed at the beginning of the transition state and at the same time as the mission of a control signal which activates the cleaning device.
In the event that there is a very large quantity of ink in the inking unit, the removal of the ink from the inking unit requiring a comparatively longer time, and in the case of an inking unit roller which is to be changed-over being placed far away from the cleaning device in the inking unit roller train, the action of changing-over the roller can be performed at the end of the transition state and, for example, at the same time as the issuance of a control signal which triggers a renewed input of ink following the cleaning of the inking unit.
The printing machine according to the invention, having a printing form cylinder and having an inking unit which inks the latter and which includes at least one inking unit roller drivable by a rotary drive at a differential speed with respect to the peripheral speed of the printing plate cylinder, is distinguished by the fact that the at least one rotary drive of the at least one inking unit roller is constructed so that it can be changed-over or shifted, based upon the timing of various operating states of the inking unit, so that the rotary drive drives the inking unit roller at the differential speed in a first operating state of the inking unit, and drives the inking unit roller at another relative speed in a second operating state of the inking unit.
The inking unit of a printing machine constructed in this way is subjected to considerably lower wear than is the case in printing machines constructed in accordance with the prior art. Because of the increased service life of soft-covered inking unit rollers, operational faults which occur between the regular maintenance intervals and are caused by any wear of these inking unit rollers are virtually ruled out during the operation of the printing machine. As a result of the increased long life of the inking unit, the printing machine is very easy to service. Because the soft-covered inking unit rollers no longer have to be replaced so frequently as a result of wear, reduced maintenance costs result.
The rotary drive can drive a number of inking unit rollers at the same time and can be constructed so that it can be Changed-over based upon the timing of the various operating states of the inking unit, so that the inking unit rollers rotate at the differential speed in a first operating state of the inking unit, and rotate at another relative speed in a second operating state of the inking unit.
The rotary drive can be a main electric motor drive of the printing machine, which also drives the printing form cylinder, and which drives the several inking unit rollers via a gear transmission mechanism. Each of the several inking unit rollers preferably has its own electric motor rotary drive assigned to it.
Both in the case of the varying embodiment of the drive or so-called drive variants having a rotary drive which can be changed-over for a number of inking unit rollers, and in the case of the drive variant having a number of inking unit rollers, respectively, driven by a rotary drive which can be changed-over, it is possible for the inking unit rollers to rotate with different, stepped differential speeds in the first operating state.
The advantage of the inking unit which includes a number of inking unit rollers, which are driven at the differential speed by the one rotary drive or the number of rotary drives in the first operating state, and are driven at the other relative speed in the second operating state, is that the printing ink processed in the inking unit is not only rolled but is also crushed in the peripheral direction of the inking unit rollers. As a result, a detrimental surface structure of the film of printing ink, the so-called orange-peel structure, is avoided in the first operating state; this structure could occur if the inking unit rollers were to roll on one another and on the printing plate cylinder at the same peripheral speed.
If the first operating state of the inking unit represents the inking of the printing form, or printing by using the printing form, a considerably higher print quality is achieved by the aforedescribed construction of the inking unit. Tests or trials have shown that if the inking unit rollers roll at a peripheral speed ratio of 1:1 in relation to one another, this is inadequate in many cases to ink an area or half-tone points homogeneously. By using a number, i.e., a plurality, of inking unit rollers in the inking unit being driven formlockingly or positively and with slippage in relation to the rollers adjacent thereto, smoother inking is possible, this improvement making itself noticeable in particular in short or anilox inking units in a comparatively low number of ink applicator rollers inking the printing form.
Such a short or anilox inking unit is described, for example, in the published German Patent Document DE 42 30 090 C2, the first and second ink applicator rollers of a total of four existing ink applicator rollers being employed for inking in the short or anilox inking unit operating mode, and the third and fourth ink applicator rollers being thrown off the printing form.
If the printing machine is an offset printing machine, and a dampening unit for dampening the printing plate is associated with the inking unit, a particularly stable printing ink/dampening solution emulsion is achieved by the large number of inking unit rollers rotating at the differential speed in the first operating state, the dampening solution being worked even better into the printing ink and into the print-free points on the printing form.
The fact that the several inking unit rollers which can be changed-over, respectively, have their own electric motor rotary drive provides a particularly beneficial possibility of driving and adjusting the rotary drives independently of one another in terms of the speed thereof.
The printing machine according to the invention permits the method according to the invention to be performed, and permits the advantages particular to the method to be realized.
The printing machine is preferably constructed as a rotary offset printing machine.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method of operating a printing machine, and a printing machine for performing the method, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: